use opacity of brush properly. the 'scatterin' will help u to give skin texture below the eye use mouse-as a device .it helps u to give skin texture,don' use airbrush more, make the brush of size 2-4 and try to wave it in direction skin time to time

in realism never make sharp outline , it should fade with the surrounding colors n eyes are never pure white n follow the ref pic carefully n use the same shadings , u will find the way , so far so good 5/5